On-board sound became very popular in 1994 when QSI introduced a high-quality, low-cost sound system for three-rail O'Gauge locomotives and when the Lionel Corporation introduced a competitive digital system about the same time. In only about three years, sound was offered in almost all top-of-the-line three-rail O'Gauge locomotives and was starting to appear in the low-end model three-rail locomotives as well.
The advent of inexpensive on-board digital sound for three-rail O'Gauge trains only became possible and popular when small affordable digital microprocessors became available that would allow sufficient sound processing within the limited space of model train locomotives. Sufficient space within the locomotive was not only needed for the electronics but was also required for acoustic sound quality and speaker placement. As the three-rail O'Gauge manufacturers began to install sound in smaller O'Gauge engines, they were forced to use smaller speakers, which often sacrificed sound quality.
A typical sound installation is shown in FIG. 1 for an O'Gauge three-rail diesel in this partial cut-away view of cab and chassis. Most three-rail O'Gauge engines have two vertically mounted DC “Can” permanent magnet motors 100 and 101 mounted directly over the diesel trucks 102 and 103 with worm and worm gears to drive one of the metal axles directly in each truck. The other axles in the trucks are linked to the driven axle with spur gears so all or most of the locomotive's wheels have power. Flywheels, 104 and 105, are often added to the motor shafts to provide coasting action should power be lost. It is also believed by most customers that the flywheel improves low speed performance. The motors are powered and controlled by the Sound and Motor Drive Electronics 106.
The chassis, motors and electronics are enclosed by the diesel body, 109 (also called a diesel cab). There are three popular diesel cab styles, wide-bodied cabs, 1700, as shown in FIG. 17, narrow-bodied cabs with high hoods, 1800, as shown in FIG. 18 and narrow-bodied cabs with low hoods, 2700 as show in FIG. 27. All three diesel types have about the same chassis width as measured at the engineers cab area, 1701,1801, and 2701 even though the hood or body width, W-1, W-2, W-3, varies. The narrow-bodied types of engines have outside walkways along the sides of the hooded area that make up the extra width. The wide-bodied diesels have the advantage of more interior space for electronics, speakers, and motors. The narrow-bodies, however, are more popular and account for larger variety and larger number of prototypes and models manufactured and sold.
Model diesel cabs are usually made of injection molded plastic although brass cabs are also popular albeit expensive and a few die-cast cabs have been produced as well. The diesel cabs may also have openings that can affect the sound quality such as the fans, 1703 and 1803, and ventilation vents or grills, 2702, 2703 and 1702, 1802, and their counterparts on the other side of the body, 1704 and 1804, not visible in the views shown in FIGS. 17 and 18. Other possible openings are the windows, portholes on the side, smoke stacks, etc. Engine models, like electric locomotives (GG-1, EP-5, E-33, etc.) have similar drive methods and sound issues as diesels. Cabs for electric locomotives also include wide body and narrow body types.
The vertical motor layout shown allows sufficient room between the motors 100 and 101 to mount a full-featured sound and motor control electronics board, 106. A single speaker 107, is usually mounted facing down or facing up in the fuel tank area below the chassis 156. It is either sealed face up to a vent hole in the chassis, 110, or mounted face down and sealed to the bottom of the fuel tank, 108, and covering venting holes 111. In either case, the speaker's front wave and back wave are separated. When mounted facing up, the front wave is vented into the sealed diesel cab area and the back wave is vented to the outside through the holes in the bottom of the fuel tank. When mounted facing down in the fuel tank, the front wave exits through the series of holes, 111, and the back wave enters the sealed diesel cab area through vent hole 110. The diesel cab area or “interior volume” defined by the chassis, 156, and diesel body 109 acts as a resonate cavity and improves both the base response and the audio volume. There appears to be little difference in sound quality between mounting face-up or face-down. However, for narrow-bodied diesels, the vent hole, 110, must have a diameter less then or equal to the interior width of the diesel cab which will partially block the speaker's front wave if the speaker is mounted face-up. Since the fuel tanks have about the same width, a full width speaker can be mounted face-down in most diesel types.
To avoid confusion between what we mean by back wave and front wave, we will restrict our examples to the method where the speaker is mounted face-down with front wave exiting to the outside through the holes, 111 and back wave entering the cab area through hole 110.
One advantage of using vertical motors mounted directly over the trucks is that it provides an unencumbered interior space above the fuel tank to allow sound to enter the cab area and sufficient room to mount the sound circuit board, 106, to the chassis surface, and to allow heat sinking the circuit board to the metal chassis as required. The circuit board width and mounting are generally designed to allow sound to pass around the circuit board and/or around the mounting studs, 175, to utilize as much of the diesel cab volume as possible.
Sound installation in smaller gauge engines: It becomes more difficult to use the same motor and flywheel design for smaller gauge engines like HO and N scale, which, in turn, requires different designs for sound systems, acoustics and speaker installation. There is little difficulty in achieving high quality acoustic sound design for most steam engines since the sound can be installed in the tender in the same way it is done for O gauge steam locomotives as shown in FIG. 25. (In FIG. 25, speakers, 2531 are mounted in the tender, vented out the chassis vent holes 2532. An audio electronics/motor control circuit board 2506 connects to a motor 2500 in the locomotive 2501 which, in turn, drives gear tower 2512 to drive the wheels.) However, installation in HO diesels and electrics, and in particularly, in narrow body, low hood types is problematic. This can be better understood by examining how most HO drive systems operate.
The most common type of motor and drive train for HO and N type engines is shown in FIG. 2. Instead of two vertical motors, each with flywheels, only one horizontal motor, 200, is used with two flywheels, 204 and 205, mounted on the front and rear motor shafts. Power is transmitted through drive shafts, 216 and 217, through telescoping universal joints 214 and 215, to gear-towers 212 and 213, that in turn power the trucks 202 and 203, respectively. The telescoping universal joints 214 and 215 allow the trucks sufficient rotation and vertical motion to navigate through curved and uneven track. The drive shafts, 216 and 217, are connected to the metal flywheels at mounting assembly points 219 and 220 to ensure that the drive shafts are locked to rotate with the flywheels.
The motor, 200, is usually mounted directly to the chassis 256. In many designs, the motor is mounted low into the fuel tank area, 208, to provide a lower profile, lower center of gravity and more headroom for circuit board, 206. The fuel tank area is often filled in with metal to increase the engine weight with a decorative outer plastic shell to provide model detail. By definition for this patent, the term “drive-train”, as distinct from the motor and trucks, constitutes the components of motor shaft, and driveline, and depending on the design may include one or more of flywheel(s), universal joint(s), gear-tower(s), gear tower(s) driveline support(s), pulley(s) and belt(s). In other words, the drive-train generally can be said to connect the motor to the truck(s).
Because the fuel tank is usually solid and because the motor sits directly over the fuel tank, there is little or no room in the tank area to mount speakers or to vent the back wave into the cab interior volume, to improve the sound quality. In addition, the fuel tank is close to the track in HO and N scale locomotives, which will cause too much sound energy to reflect back and degrade the sound quality and volume. To mitigate these problems, speakers are often mounted on the inside of the cab, directly interior of decorative grills or fan openings, such as 1703, 1702 in FIG. 17 and 1802 and 1803 in FIG. 18, and 2703 and 2702 in FIG. 27, to vent the sound directly to the outside. Vent and fans are often limited in surface area, however, or are shaped in a way that does not allow the maximum speaker area possible to vent sound to the outside and the resultant sound quality and volume are poor. It is desirable to use the largest speakers possible, which is not always consistent with the available grill and vent area for particular locomotive models.
In addition, because the motor is not directly mounted over the trucks, there is usually more opportunity for the back wave to escape through large openings needed for the gear tower or other truck drive mechanisms to rotate as the truck turns to negotiate through curved track. These gear tower holes are shown by open areas 221 and 222 in FIG. 2 and in FIG. 4, which shows a top view of the chassis with cab removed. Any sound escaping through these holes can easily be propagated to the outside through the open truck assemblies, 202 and 203. Mixing of back wave and front wave from these open areas, 221 and 222, over the trucks further degrades the sound quality.
Another restriction in the acoustic design is the space consumed from added metal weights. These weights are used to increase the overall tractive force of the engine and are sometimes used to hold or support lamps, lighting boards, electronic circuit boards (such as DCC decoders), etc. within the engine's interior. Any acoustic design must not compromise the pulling power or other features of the locomotive too severely or it will decrease the desirability of the engine.